1. Field of the Invention
This invention relates to adhesion promoting organosiloxane compositions. More particularly, this invention relates to adhesion-promoting compositions that cohesively bond cured organosiloxane materials such as elastomers and resins to organic polymers during curing of the materials by a hydrosilation reaction or by the reaction of silanol groups with hydrolyzable groups such as alkoxy in the presence of moisture. The compositions do not contain the objectionable ingredients associated with prior art adhesion promoting compositions.
2. Background Information
U.S. Pat. No. 4,719,262, which issued to Edwin Plueddemann on January 12, 1988 describes organosilicon compounds useful as primers. One group of organosilicon compounds comprises bis-silylalkanes of the formula (OR").sub.3-x (R'O).sub.x SiRSi(OR').sub.x (OR").sub.3-x where R represents an alkylene radical, OR' represents an alkoxy group, OR" represent substituted or unsubstituted alkenyloxy, alkenyloxyalkoxy, or carboalkenyloxyalkoxy groups, where the ethylenic unsaturation is located at terminal carbon atoms, and x is 1 or 2. This patent also teaches improving the performance of the disclosed organosilicon compounds as bonding agents by combining them with (A) copolymers derived from 1) ethylenically unsaturated organic compounds such as esters of acrylic and methacrylic acids, and 2) ethylenically unsaturated alkoxysilanes, and (B) organohydrogensiloxanes as crosslinking agents for the copolymer.
The copolymers referred to as A in the aforementioned patent are described in U.S. Pat. No. 3,306,800, hereinafter referred to as the '800 patent, which issued to Edwin Plueddemann on Feb. 26, 1967.
Primers and adhesion promoters containing the combination of the aforementioned ingredients A, B and the bis-silylalkanes described in the Plueddemann patent U.S. Pat. No. 4,719,262 provide excellent adhesion between organosiloxane elastomers and amorphous organic polymers such as polymerized esters of acrylic or methacrylic acids, polycarbonates and polystyrene. Primer compositions containing these ingredients in combination with a solvent selected from ethylenically unsaturated alcohols containing from 4 to 6 carbon atoms are described in U.S. Pat. No. 4,795, 775, which issued on Jan. 3, 1989.
A disadvantage that may prevent wide acceptance of adhesion promoting compositions described in U.S. Pat. Nos. 4,795,775 and 4,719,262 is the toxicity of some organosilicon compounds containing the bis-silylalkyl group that are used to prepare the adhesion-promoting ingredient described in these patents. This disadvantage has stimulated a search for less toxic organosiloxane adhesion promoters suitable for use with organosiloxane elastomers that cure by a platinum catalyzed hydrosilation reaction and by the reaction of silanol groups with alkoxy or other silicon-bonded hydrolyzable groups in the presence of moisture and a suitable catalyst.
Primer compositions containing various combinations of organosilicon compounds with alkyl orthosilicates and/or organohydrogensiloxanes are described in the prior art.
Coatings formed from (meth)acrylate polymers containing pendant alkoxysilyl groups are described in U.S. Pat. No. 4,491,650, which issued on Jan. 1, 1985. The polymers are prepared by reacting a poly(meth)acrylate containing pendant hydroxyl groups with an isocyanato-functional alkoxysilane.
Canadian Patent No. 2,069,564, which issued on Dec. 14, 1992 describes primer compositions containing an alkoxysilane that optionally contain a reactive organic group bonded to silicon, an organotitanate and a tin salt of a carboxylic acid.
Primer compositions containing an organotitanate in combination with either an organosilicon compound containing at least 2 silicon-bonded alkoxy groups or an organohydrogensiloxane that optionally contains silicon bonded alkoxy groups are described in U.S. Pat. No. 4,749,471.
Japanese patent publication no. 86/004865 describes primer compositions containing an organosilicon resin, an organohydrogensiloxane and an organotitanate.
Japanese patent publication no. 91/031266 describes a primer for the copier rolls of an electrostatic copier. The primer contains an organosilicon compound with alkenyl groups, an organohydrogensiloxane, a platinum-containing hydrosilation catalyst and an organotitanate.
Applicant's copending applications Ser. Nos. 08/160132 and 08/160134, both filed on Dec. 2, 1994 describe adhesion promoters wherein one of the ingredients is a copolymer of the class described in the aforementioned '800 patent and contains repeating units derived from a) an ethylenically unsaturated organic compound and b) a silane containing an ethylenically unsaturated group. Compositions that cure by a platinum-catalyzed hydrosilation reaction in the presence of a platinum group metal or a compound thereof at temperatures of at least 70.degree. C. require an organohydrogensiloxane in addition to the aforementioned copolymer. When the compsition is cured at lower termperatures the presence of an alkyl orthosilicate and an organotitanate is required to achieve adequate bonding to the substrate, resulting in failure within the cured elastomer rather than at the interface between the elastomer and the substrate.
Subsequent work by the present inventor revealed that the best adhesion to both types of curable organosiloxane compositions described in the aforementioned copending patent applications to a variety of substrates was achieved using tetra(2-methoxyethyl)silane, also referred to as methylcellosolve orthosilicate. A disadvantage associated with use of this silane is the relatively high toxicity ascribed to the 2-methoxyethanol generated during hydrolysis of the silane.
One objective of this invention is to define a class of adhesion promoting compositions that will cohesively bond organic polymers to organosiloxane materials, particularly elastomers and resins, that are in contact with the primer layer during curing of these materials. The adhesion promoting compositions do not contain any of the organosiloxane compounds considered objectionable based on the relatively high toxicity of intermediates and/or by-products associated with these compounds.